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How to Read a TV Schematic

Schematic diagrams for radios, TVs, and other electronic devices are a road map showing how individual components are connected together. Technicians use schematics for troubleshooting problems and making repairs. Each component -- resistors, capacitors, transistors, and so on -- has a standard symbol that represents that component. These symbols are generally universal, allowing schematic diagrams to be read by even the amateur hobbyist.

Things You'll Need

Schematic diagram
Schematic symbol chart
Multimeter (optional)
Oscilloscope (optional)

Instructions

- 1
  Learn the schematic symbol for the electronic components found in a TV (see References). There aren't very many to learn, and most symbols are logical pictorials of the component's function. A sawtooth-like zig-zag line, for example, indicates a resistor, which "resists" or makes a rough road for the current passing through it. Learn what each physical component looks like and the schematic symbol that represents it.
- 2
  Identify specific components in the TV by their schematic location. Many times a printed circuit board will have letter and number designations which will match the schematic. For example, R1 and R2 will be resistors, and C1 and C2 will be capacitors. The schematic diagram will also show the value of components, such as ".01uf" for a capacitor or "330 ohms" for a resistor. Capacitors often have their value physically printed on the capacitor itself. Resistors use three or four color-coded bands to identify their value. Integrated circuits and transistors will have a number on both the component and the schematic.
- 3
  Follow the signal flow, which is generally left to right on a schematic diagram. The RF (radio frequency) antenna input is typically shown on the left, and as the signal is processed it moves in a path of circuitry to the right. Think of the TV's functions as blocks or sections, with the RF input, color, video, sync, sound and remote control sections.
- 4
  Isolate the section of the schematic that deals with the area of the TV in which you are interested. For example, if your TV has no sound, look for the section on the schematic diagram that shows the circuitry for audio.
- 5
  Compare voltage test points shown on the schematic to readings on your multimeter. Many TV schematics will include voltages at different locations, especially in the power supply section. Use these voltages when troubleshooting problems.
- 6
  Match schematic waveform points to those in the TV using an oscilloscope. Schematics that are designed for repair technicians may show small thumbnail snapshots of waveforms at critical points. Placing the probe from an oscilloscope at these points will reveal if there is a problem.

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